The present invention relates to a method for inducing audio vibrations e.g. buzzes, rattles, and other noise in the interior of a vehicle in order to determine the source of such noise within the vehicle. In particular, the invention relates to the use of an FM broadcast transmitter to transmit audio frequency sine waves to an FM receiver in the interior of the vehicle in order to induce sympathetic vibrations, e.g. buzzes and rattles, from equipment in the interior of the vehicle that may be a source of noise during normal use of the vehicle.
Within a vehicle, sounds and vibrations from radio loudspeakers, the engine and other normal internal and external equipment produce sympathetic vibrations in neighboring items, such as trim panels, instrument panel components, etc., just as a tuning fork excites a piano string. Sympathetic vibrations within a vehicle are often heard as buzzes that seem to be random in time and space, or may beat in time to musical programming.
Although the presence of small, frequency-sensitive buzzes may appear inconsequential, their net effect is to detract from the customer's perception of overall vehicle and sound system quality. Thus, particularly in the automotive industry, there is a need for a system to induce these annoying buzzes so that their sources can be identified and modified so as to reduce or eliminate them.
U.S. Pat. No. 5,245,664 to Kinoshite et al. discloses an active noise control system. The system includes a plurality of vibration pickups for detecting noise sources. A controller, responsive to the detected noise sources, generates "control sounds" or "anti-noise" to interfere with or cancel the effect of the detected noises. U.S. Pat. No. 4,829,590 to Ghose, U.S. Pat. No. 5,170,433 to Elliot et al., and U.S. Pat. No. 5,222,148 to Yuan disclose similar types of systems. These patents, however, do not address the problems associated with identifying sources of the noise so they can be physically modified to eliminate the noise. That is, the systems do not provide a method or means to induce noises from sources within a vehicle to allow designers and developers the opportunity to remove or modify the sources of the noise.
In a typical prior art system, audio generators placed in a vehicle under test are used to induce sympathetic vibrations. According to one known prior art system, audio frequency tones which are swept over a range of frequencies are recorded on standard audio cassettes. These cassettes are played through the vehicle's sound system to induce the vibration of potential noise sources, and they do not allow precise control over the frequency generated. In particular, the operator cannot pause at a particular frequency while the source of noise is tracked down. This system improves the repeatability of tests over those made with noise generators and allows for correlation of test results. While the sweep frequency recordings standardize testing somewhat, they do not provide a constant and exact audio frequency source, and they do not allow precise control over the frequency generated. In particular, the operator cannot pause at a particular frequency while the source of noise is tracked down. The cassettes also require that the vehicles to be tested have operating cassette players, which players are not available in many low-end models of vehicles.